Diesel fuel really doesn't gel when cold. Under very cold conditions, some of the heavier molecules crystallize or "precipitate" out of the mix. This leaves zillions of small crystals of a waxy substance in the fuel that floats down the fuel line and gets glommed up in the fuel filter. If you were to take a fuel filter off and pour out the collected mess, it looks like a gelatin, hence the term "gelled-up"
Add a little heat, it goes back into solution, and burns up with the rest of the fuel.
Modern distillation is better than it used to be, and there are now much fewer of the heavier molecules in the newer diesel, mostly because the heavier elements don't burn as clean, and the EPA says they have to go. So...not as much gelling as in years past. Those heavier molecules also were the better lubrication in the diesel. Having been removed from the newer fuel, the fuel companies now must put in additives to increase the lubrication qualities of the fuel. That is also why diesel costs more than gasoline now. 20 years ago, the fuel distillers could take all the stuff that was too heavy for gasoline and mix it into the diesel. Not anymore!
Overall: it's not a good idea to use old-school cold weather solutions on the newer diesel.